common/scsi_debug: use udevadm settle instead of sleeping

common/scsi_debug: use udevadm settle instead of sleeping

The variable UDEV_SETTLE_PROG is already defined and used for
lvm to either use `udevadm settle` in case it is available, and
if not, use 'sleep 1' otherwise (ancient distros or CONFIG_NET
is missing).

Use it on scsi_debug to replace the sleep calls sprinkled in
place after module removal. The correct thing to do is to
just use udevadm settle when available, and only fall back to
calling sleep when udevadm is not available or CONFIG_NET
is disabled.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>